Rotating components may be unbalanced as manufactured, and balancing techniques are utilized to balance these components to minimize vibrations and enhance component life. The term “unbalanced” means that the center of mass and/or the inertial axes of a rotating object are not aligned with the axis of rotation of the rotating object. Static unbalance can be expressed in terms of the distance of the center of mass of the rotating object from the axis of rotation, and the angular location of the center of mass with respect to the axis of rotation. Dynamic unbalance is present when the axis of mass or inertia of a rotating object does not intersect the shaft axis.
Apparatuses for measuring unbalance are well known, and generally fall into one of two classes: static balancers and dynamic balancers. One known balancing system drives a rotatory element about a fixed axis of rotation. A sensor outputs a signal indicating the rotational position of the rotary element while an unbalance measuring arrangement outputs an unbalance data signal that represents the magnitude of a residual unbalance characteristic of the rotatory element. An unbalance correction operation is performed, such as by removing a specific amount of material from the rotary element at a specific location, where the amount and location of the material to be removed are determined using the position signal and the unbalance data signal. The effect of the balance correction(s) is to move the rotor mass center onto the axis of rotation and/or align the inertial axes with the axis of rotation.
Balancing techniques are applicable to turbocharger components. Turbochargers are forced induction devices for internal combustion engines that utilize pressurized exhaust gas to increase the pressure of intake air. Pressurizing the intake air allows for higher compression by forcing more air and fuel into the cylinders of the engine. This allows for increased power output from the engine as compared to a naturally aspirated engine.
The exhaust gas from the engine is routed to a turbine housing of the turbocharger. A turbine wheel is located inside the turbine housing. The turbine wheel is connected to a shaft, for example, by welding. As the exhaust gas passes through the turbine housing, the exhaust gas causes the turbine wheel to spin. As an example, some turbocharger turbine wheels spin at speeds in excess of 250,000 revolutions per minute.
A compressor wheel is fastened to the shaft at the end opposite to the turbine wheel. The compressor wheel is enclosed in a compressor housing. Rotation of the turbine wheel causes a corresponding rotation of the compressor wheel. As the compressor wheel spins, intake air is drawn into the compressor housing. The intake air is pressurized by the compressor wheel, and is then routed to the engine.
As a result of the high rotational speeds, the rotating components of the turbocharger must be balanced with respect to their axis of rotation. If these components are unbalanced, components of the turbocharger can fail prematurely, and sometimes catastrophically. Balancing of turbocharger components can be performed with mass removal techniques. However, the materials used in turbocharger components, and in turbocharger wheels in particular, are difficult to machine via conventional methods with the precision required to make effective balance corrections.